Transit systems are well known in the art. Some conventional transit systems implement linear induction motors (LIM's) wherein the LIM primaries are located at spaced intervals between the rails of a track and wherein the LIM secondaries or reaction rails are secured to the chassis of vehicles travelling along the track. These transit systems are conventionally designated as LIM in-track transit systems. In these in-track transit systems and as in all transit systems, when more than one vehicles are travelling along the track, it is important to avoid collisions between vehicles. This of course requires the speed of all vehicles travelling along the track to be accurately controlled to ensure that vehicle spacing is maintained. In many systems, to increase vehicle throughput, the vehicles are propelled at high speeds. However, typically in certain segments of the track such as curves, track switches, etc., high speeds are not permitted due to the possibility of derailment. Accordingly, deceleration zones are provided adjacent these sections of track to slow the vehicles so that they travel through these sections of track at a safe speed.
In conventional systems, closed loop control has been implemented in the deceleration zones using multiple LIM primaries and associated controllers therefor. Although these components provide excellent vehicle control, a problem exists in that if the linear induction motor primaries and/or controllers fail, vehicles are not slowed at all (except due to friction and drag) in the deceleration zone and thus, may enter the following sections of the track at unsafe speeds. Furthermore, another problem exists in that the controllers and LIM primaries are expensive and thus, conventional systems using multiple LIM primaries increase construction and operation costs of the transit system.
A prior art in-track transit system is shown in U.S. Pat. No. 4,716,346 to Matsuo which discloses a conveying apparatus including a track having a curve and a carriage movable along the track. The track is provided with a plurality of LIM stators disposed along the straight portions of the track. A reaction rail is secured to the chassis of the carriage and communicates with the stators. Carriage detection sections are also located on the track and are positioned before and after the curved segment of the track. The carriage detection sections co-operate with the LIM stators and detect the speed and mass of the carriage. When a moving carriage passes over a carriage detection section, the speed of the carriage is calculated. A predetermined reverse thrust is then provided to the carriage via an energizing LIM stator and the speed of the carriage is once again calculated. This allows the mass of the carriage to be determined so that the maximum speed of the carriage over the curved section of track can be determined. Once the maximum speed has been calculated, it is compared with the speed of the carriage so that the necessary thrust can be applied to the carriage to ensure that the vehicle travels at the correct maximum speed over the curved segment of track.
As can be seen, the carriage detection sections in the Matsuo system require two controllers and two LIM stators to permit the mass of the carriage to be calculated so that the second LIM stator is capable of being operated to supply the necessary thrust to the carriage, thereby ensuring the carriage to travel along the curved section of the track at the desired speed. It should be apparent that if the controllers or LIM stators in the Matsuo system fail, the carriage is not slowed prior to entering the curved section of the track. Furthermore, the cost of the multiple controllers and LIM stators makes this type of velocity control zone expensive.
It is therefore an object of the present invention to obviate or mitigate the above disadvantages by providing a novel deceleration zone in a linear motor in-track transit system.